Pneumatic spindle with means to direct the bearing air towards the tool-holding collet

ABSTRACT

A spindle ( 1 ) in which the moving part ( 2 ) fixed to the tool-holding collet ( 3 ) is supported by one or more aerostatic bushes ( 4 ) on cushions of air generated by a jet of compressed air that circulates continuously along the air gaps ( 5 ) between the aerostatic bushes ( 4 ) and the moving part ( 2 ) and passes out of the spindle ( 1 ) through the co-axial aperture ( 6 ) formed in a flange ( 7 ) through which the tool-holding collet ( 3 ) projects from the spindle ( 1 ). Directing elements ( 8 ) are attached to the outside of the flange ( 7 ) to collect the air passing out of the abovementioned aperture ( 6 ) and cause it to adopt an outward direction of motion (E) that is tangential to or incident on the terminal part ( 3   t ) of the tool-holding collet ( 3 ) and roughly parallel to the axis of the spindle ( 1 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

This is the 35 USC 371 National Stage of International ApplicationPCT/IB03/00366, filed on Feb. 4, 2003, which designated the UnitedStates of America.

BACKGROUND OF THE INVENTION

The present invention relates to machine tools, and more especiallythose designed to drill holes at very high speeds of rotation of thetool (even exceeding 100,000 revolutions per minute).

More specifically, the invention is concerned with machine tools inwhich, to prevent friction between the spindle casing and the rotatingparts fixed to the tool, aerostatic bushes, known to those skilled inthe art, are interposed between the two. In aerostatic bushes therotating parts are supported by cushions of air generated in the airgaps by the continuous feeding in of a jet of air which, after havingtravelled through the said air gaps performing its bearing function asdescribed, passes out of the spindle through the same aperture formed ina flange mounted on the free end of the spindle, as that through whichthe tool-holding collet projects.

In the high-speed drilling work mentioned above, and especially wherethe holes are being made in materials of low specific weight such as theresins for printed circuit boards, a fine dust is thrown up, consistingof the minute chips that are generated, which is deposited in the radialslits formed in the end of the tool-holding collet to enable it to beopened and closed around a tool. This necessitates cyclical cleaning andmaintenance operations, which, in view of the large total number ofspindles usually used in a plant and the frequency of the drillingoperations, represents a significant addition to production costs. Thereason for this is that although the aforementioned jet of air passesout through the said aperture parallel to the tool-holding collet, it isthen deflected by vortices generated by the very high-speed movement ofthe edges and sides of the collet and begins to move in a directionwhich has a large radial component leading away from the said collet. Itcannot therefore exert any action that would keep the said fine dustaway from the abovementioned radial slits.

In other words, in front of the end of the collet, a zone is generatedin which the air is effectively stagnant, allowing the granules of thesaid fine dust to pass through it and reach and be deposited in theabovementioned slits.

SUMMARY OF THE INVENTION

The inventor of the present invention felt that this problem could beavoided if the abovementioned jet of air could be directed by suitablemeans to keep it alongside the tool-holding collet, before it comes awayfrom it in a tangential direction roughly parallel to the axis of thespindle.

For this purpose he has devised the spindle according to the invention,in which directing means are attached to its flange, through which thetool-holding collet projects, which means collect the said jet of airand channel it into a direction that is tangential to or incident on theterminal part of the said tool-holding collet containing the said slits.The jet of air thus keeps the fine chip dust away from the slits,thereby achieving the object of keeping them clean.

The subject of the present invention is therefore a spindle as describedbelow.

A more detailed description will now be given of a preferredillustrative embodiment of a spindle according to the invention. Thisembodiment is selected from the many embodiments available to thoseskilled in the art in keeping with the below teachings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the course of the description, reference will also be made to theattached drawings, which show:

in FIG. 1, a longitudinal section through a spindle with aerostaticbushes in accordance with the prior art; and

in FIG. 2, a longitudinal section through a spindle with aerostaticbushes in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, this shows that, in a spindle 10 in accordance withthe prior art, the moving part 2, which is integral with thetool-holding collet 3 in its rotations R, is supported by two aerostaticbushes 4 via two cushions of air generated by known methods by a jet ofcompressed air flowing continuously (arrows D) through the air gaps 5between the aerostatic bushes 4 and the said moving part 2. This jet ofair then passes out of the spindle 10 through a co-axial aperture 6formed in a flange 7 through which the tool-holding collet 3 protrudesfrom the casing 10 c of the spindle 10. As can be seen in the drawing,after passing through the aperture 6, the abovementioned jet of airadopts a direction (again indicated by the arrows D) that has asignificant radial component causing it to move away from the terminalpart of the tool-holding collet 3 and its radial slit 3 t. The jet ofair cannot therefore exert any action that would keep the fine chip dust(not shown) away from the slits.

FIG. 2, on the other hand, shows a spindle 1 according to the invention,similar in type to that described earlier, and having the same componentparts, namely a casing 1 c and two aerostatic bushes 3 which support asillustrated the moving part 2 which is integral in its rotations R witha tool-holding collet 3 containing the said radial slits 3 t. In thespindle 1 according to the invention, however, directing means,consisting here of a cap 8, are attached co-axially to the outside ofthe flange 7 (which is similar to that described in the previous case).These directing means collect the said jet of air (the direction ofwhich is indicated this time by the letter E) and channel istangentially to or in a slightly incident manner on the terminal part ofthe tool-holding collet 3 containing the abovementioned radial slits 3t, which collet projects out of the cap 8 to at least some degree,sufficient for its opening up to release the tool (not shown) not to beobstructed by the presence of the cap 8.

As seen in FIG. 2, as the jet of air passes out through the gap betweenthe cap 8 and the tool-holding collet 3, it maintains a direction E thatis tangential to or slightly incident on the terminal part of the colletcontaining the said radial slits 3 t, thus preventing fine chip dustgetting into the slits and being deposited in them.

The object addressed by the inventor has therefore been achieved. Thisobject can also be achieved by using components (such as the cap 8, forexample) that differ in shape and position from those described aboveand shown in FIG. 2.

1. Spindle (1), comprising: an outer case (1 c) terminating at one endwith a flange (7) having an aperture (6); a moving part (2) locatedco-axially within the outer case and extending through the aperture; atool-holding collet (3) fixed to the moving part, the collet outwardlyprojecting from an end-most portion of the moving part; an air directingmeans (8) attached to an exterior surface of the flange at the apertureand surrounding the end-most portion of the moving part, an end-mostportion of the collet extending outwardly beyond an end-most portion ofthe air directing means; an aerostatic bush generating a jet ofcompressed air that forms a cushion of air circulating continuouslyalong air gaps (5) located between the moving part and the aerostaticbush and exits out of the case via a path defined by the air directingmeans at an outlet located intermediate the end-most portion of the airdirecting means and the end-most portion of the moving part, the movingpart (2) supported by the cushion of air generated by a jet ofcompressed air, wherein, the air directing means (8) is shaped tocollect the air exiting out of the outlet in a first direction and toredirect the exiting air from the first direction to a second directionwith an outward direction of motion (E) tangential to the end-most part(3 t) of the collet, the redirected exiting air moving roughly parallelto an axis of the spindle (1).
 2. The spindle according to claim 1,wherein, said directing means is a shaped cap (8) fixed to the outsideof the said flange (7), co-axially with respect to the tool-holdingcollet (3), the cap extending beyond outer most surfaces of the flangeand of the case.
 3. The spindle according to claim 2, wherein, theend-most part (3 t) of the collet comprises tapered converging sides,and the air directing means (8) is shaped to collect the air exiting outof the outlet in the first direction and to redirect the exiting airfrom the first direction to the second direction with an outwarddirection of motion (E) tangential to the tapered converging sides ofthe end-most part of the collet.
 4. The spindle according to claim 3,wherein, an air space is defined between the air directing means (8) andthe end-most portion of the moving part, the air space has a decreasingcross section, as measured orthogonal to the axis and approaching fromthe flange toward the outlet.
 5. The spindle according to claim 1,wherein, said directing means is a shaped cap (8) fixed to the outsideof the said flange (7), co-axially with respect to the tool-holdingcollet (3), the cap. having a first cylindrical portion and an attachedsecond converging tapered portion, the cap extending beyond outer mostsurfaces of the flange and of the case.
 6. The spindle according toclaim 5, wherein, the end-most part (3 t) of the collet comprisesconverging tapered sides, and the air directing means (8) is shaped tocollect the air exiting out of the outlet in the first direction and toredirect the exiting air from the first direction to the seconddirection with an outward direction of motion (E) tangential to theconverging tapered sides of the end-most part of the collet.
 7. Thespindle according to claim 6, wherein, an air space is defined betweenthe air directing means (8) and the end-most portion of the moving part,the air space has a decreasing cross section, as measured orthogonal tothe axis and approaching from the flange toward the outlet along thesecond tapered converging portion of the cap.
 8. The spindle accordingto claim 1, wherein the air directing means directs the air exiting theoutlet in the second direction that is converging toward the axis as theair exits the outlet.
 9. Spindle (1), comprising: an outer case (1 c)terminating at one end with a flange (7) having an aperture (6);. amoving part (2) located co-axially within the case and extendingoutwardly through the aperture; a tool-holding collet (3) fixed to themoving part, the collet outwardly projecting from an end-most portion ofthe moving part; an air director (8) attached to an exterior surface ofthe flange at the aperture, outwardly extending from the aperture, andsurrounding the end-most portion of the moving part, an end-most portionof the collet extending outwardly beyond an end-most portion of the airdirector; an aerostatic bush arrangement generating a jet of compressedair forming a cushion of air circulating continuously along air gaps (5)located between the aerostatic bush arrangement and the moving part, thecompressed air exiting out of the case via a path defined by the airdirector at an outlet located intermediate the end-most portion of theair directing means and the end-most portion of the moving part,wherein, the air director (8) is shaped to collect the air exiting outof the outlet and to redirect the air exiting from the outlet from afirst direction parallel to the axis to a second direction with anoutward direction of motion (E) tangential the end-most part (3 t) ofthe collet and converging toward the axis as the air exits the outlet.10. The spindle according to claim 9, wherein, said air director is ashaped cap (8) fixed to the outside of the said flange (7), co-axiallywith respect to the tool-holding collet (3), the cap extending beyondouter most surfaces of the flange and of the case.
 11. The spindleaccording to claim 10, wherein, the end-most part (3 t) of the colletcomprises tapered converging sides, and the air director (8) is shapedto collect the air exiting out of the outlet in the first direction andto redirect the exiting air from the first direction to the seconddirection with an outward direction of motion (E) tangential to thetapered converging sides of the end-most part of the collet.
 12. Thespindle according to claim 11, wherein, an air space is defined betweenthe air directing means (8) and the end-most portion of the moving part,the air space has a decreasing cross section, as measured orthogonal tothe axis and approaching from the flange toward the outlet.
 13. Thespindle according to claim 9, wherein, said air director is a shaped cap(8) fixed to the outside of the said flange (7), co-axially with respectto the tool-holding collet (3), the cap having a first cylindricalportion and an attached second converging tapered portion, the capextending beyond outer most surfaces of the flange and of the case. 14.The spindle according to claim 13, wherein, the end-most part (3 t) ofthe collet comprises converging tapered sides, and the air director (8)is shaped to collect the air exiting out of the outlet in the firstdirection and to redirect the exiting air from the first direction tothe second direction with an outward direction of motion (E) tangentialto the converging tapered sides of the end-most part of the collet. 15.The spindle according to claim 14, wherein, an air space is definedbetween the air directing means (8) and the end-most portion of themoving part, the air space has a decreasing cross section, as measuredorthogonal to the axis and approaching from the flange toward the outletalong the second tapered converging portion of the cap.